Microbes

What Are Microbes?

Microbes are tiny microorganisms, too tiny to see without a microscope. Microbes are abundant on earth, they live everywhere - in air, soil, rock, and water, and are found in plants and animals as well as in the human body. Some live happily in searing heat, while others thrive in freezing cold. Some microbes need oxygen to live, and others don't.

Most Microbes Belong to One of Four Major Groups:

• Bacteria
• Viruses
• Fungi
• Protozoa

Some microbes can make us sick causing disease in humans, plants, and animals. Other microbes are essential to us for a healthy life.

A common word for microbes that cause disease is "germs" and some people refer to disease-causing microbes as "bugs." We've all said it, "I think I've got the flu bug." That is a phrase we may hear during the wintertime to describe an influenza (the flu) virus infection.

Since the 19th century, microbes have caused infectious diseases. Near the end of the 20th century, researchers began to learn that microbes also contribute to many chronic (disorders lasting a long time, often years) diseases and conditions. Mounting scientific evidence strongly links microbes to some forms of cancer, coronary artery disease, diabetes, multiple sclerosis, and chronic lung diseases.

Microbes Have Bothered Us for Thousands of Years

Since ancient times, historians have documented infections and diseases in humans. Present-day archeologists and microbiologists (scientists who study microbes) are discovering evidence of infectious disease in prehistoric human skeletons.

In the late 20th century, researchers uncovered evidence that prehistoric humans were troubled by microbial parasites and used natural remedies against them. Along with the frozen mummy of the "Ice Man," who was found in the mountains of northern Italy and lived between 3300 and 3100 B.C., scientists found a type of tree fungus containing oils that are toxic to intestinal parasites. Later, in the laboratory, researchers found the eggs of a microscopic (too small to be seen with the naked eye) parasitic intestinal roundworm, Trichuria trichiura (whipworm), in his intestines.

Smallpox, which is caused by a variola virus, was described in ancient Egyptian and Chinese writings. According to some researchers, over the centuries smallpox was responsible for more deaths than all other infectious diseases combined. It killed millions of people over thousands of years before being eradicated (eliminated) late in the 20th century by worldwide vaccination. The last case of naturally occurring smallpox was recorded in 1977.

Evidence on a 1300 B.C. Egyptian stone engraving shows that poliomyelitis (polio) also has been around since ancient times. In the 1990s, public health officials launched a massive international vaccination campaign to eradicate the polio virus, which causes paralysis and can be deadly.

Microbes Found in the Healthy Human Body

Below are a selection of usually harmless microbes found in the body, some of which help keep our bodies functioning normally, but if their numbers become unbalanced, these microbes may make us sick:

• Ear (outer) - Aspergillus (fungus)
• Skin - Candida (fungus)
• Small intestine - Clostridium (bacteria)
• Intestines - Escherichia coli (bacteria)
• Vagina - Gardnerella vaginalis (bacteria)
• Stomach - Lactobacillus (bacteria)
• Urethra - Mycobacterium (bacteria)
• Nose - Staphylococcus aureus (bacteria)
• Mouth - Streptococcus salivarius (bacteria)
• Large intestine - Trichomonas hominis (protozoa)

Microbes "Can" Make Us Sick

According to health care experts, infectious diseases caused by microbes are responsible for more deaths worldwide than any other single cause. They estimate the annual cost of medical care for treating infectious diseases in the United States alone is about $120 billion.

The science of microbiology explores how microbes work and how to control them. It seeks ways to use that knowledge to prevent and treat the diseases microbes cause. The 20th century saw an extraordinary increase in the knowledge about microbes. Microbiologists and other researchers had many successes in learning how microbes cause certain infectious diseases and how to combat those microbes.

Unfortunately, microbes are much better at adapting to new environments than are people. Having existed on earth for billions of years, microbes are constantly challenging human newcomers with ingenious new survival tactics.

• Many microbes are developing new properties to resist drug treatments that once effectively destroyed them. Drug resistance has become a serious problem worldwide.
• Changes in the environment have put certain human populations in contact with newly identified microbes that cause diseases we have never seen before, or that previously occurred only in isolated populations.
• Newly emerging diseases are a growing global health concern. Since 1976, scientists have identified approximately 30 new pathogens.

Common Diseases and Infections and Their Microbial Causes

• Caused by Viruses
  • Chickenpox
  • Common cold
  • Flu
  • Genital herpes
  • Viral hepatitis
• Caused by Bacteria
  • Strep throat
  • Tuberculosis (TB)
  • Urinary tract infection
• Caused by Fungi
  • Athlete's foot
• Caused by Protozoa
  • Malaria
• Caused by Combinations
  • Sinusitis - caused by bacteria and fungi
  • Vaginal infections - caused by bacteria and fungi
  • Meningitis - caused by bacteria and viruses
  • Pneumonia - caused by bacteria, fungi, and viruses
  • Diarrheal disease (diarrhia) - caused by bacteria, protozoa, and viruses
  • Skin diseases - caused by bacteria, fungi, protozoa, and viruses

There Are Many Different Ways To Get Infected by Germs

• Through the Air - Coughing or Sneezing
  Common ways to get viruses that cause colds or flu, or the bacteria that cause tuberculosis (TB). International airplane travel can expose you to germs not common in your own country.
• Close Contact With Another Person
  • Kissing - Scientists have identified more than 500 types of bacteria that live in our mouths. Some keep the oral environment healthy, while others cause problems like gum disease.
  • Sexual Intercourse - Microbes such as HIV, herpes simplex virus, and gonorrhea bacteria are examples of germs that can be transmitted directly during sexual intercourse.
• Touching Infectious Material
  • Catching the cold virus from shaking someone's hand or from touching contaminated surfaces, such as a handrail or telephone.
  • Unintentionally passing feces from hand to mouth or the mouths of young children when diaper changing. Infant diarrhea is often spread in this way. Day care workers, for example, can pass diarrhea-causing rotavirus or Giardia lamblia (protozoa) from one baby to the next between diaper changes and other childcare practices. It is especially important to wash your hands before preparing or eating food, after coughing or sneezing, after using the bathroom, and after changing a diaper.
• A Healthy Person Can Carry Germs and Pass Them To Others
  A person can pass germs on to others, yet not be affected by those germs. For example, the germs of Salmonella typhi bacteria, which cause typhoid fever, are usually spread through food or water. A person can carry the Salmonella bacteria and have no symptoms of the disease, but can spread the disease to others through the food they prepare.
• Animals, Especially Household Pets
  • The rabies virus, which can infect cats and dogs, is one of the most serious and deadly of these microbes. Thank goodness, rabies vaccine prevents animals from getting rabies. Vaccines protect people from accidentally getting the virus from an animal. They also prevent people who already have been exposed to the virus, such as through an animal bite, from getting sick.
  • Dog and cat saliva can contain any of more than 100 different germs that can make you sick. Pasteurella bacteria, the most common, can be transmitted through bites that break the skin causing serious, and sometimes fatal, diseases such as blood infections and meningitis. Meningitis is the inflammation of the lining of the brain and spinal cord. Warm-blooded animals are not the only ones that can cause you harm. Pet reptiles such as turtles, snakes, and iguanas can give Salmonella bacteria to their unsuspecting owners.
• Mosquitoes, Fleas, and Ticks
  • Mosquito - Malaria, Dengue Fever, West Nile Virus, Viral Encephalitis - Mosquitoes may be the most common insect carriers, also called vectors, of pathogens (disease-causing organisms). Anopheles mosquitoes can pick up Plasmodium, which causes malaria, from the blood of an infected person and transmit the protozoan to an uninfected person.
  • Flea - Plague - Fleas that pick up Yersinia pestis bacteria from rodents can then transmit plague to humans. Today, modern antibiotics are effective against plague, but if an infected person is not treated promptly, the disease is likely to cause illness or death.
  • Tick - Babesiosis, Ehrlichiosis, Lyme Disease, Relapsing Fever, Colorado Tick Fever, Rocky Mountain Spotted Fever - Ticks, which are more closely related to crabs than to insects, are another common vector. The tiny deer tick can infect humans with Borrelia burgdorferi, the bacterium that causes Lyme disease, which the tick picks up from mice.
• Food or Water
  • Food - Eating contaminated foods, some of which can be fatal if not treated properly.
  • Water - Cryptosporidia are bacteria found in human and animal feces and can get into lake, river, and ocean water from sewage spills, animal waste, and water runoff. Millions of Cryptosporidia can be released from infectious fecal matter. People who drink, swim in, or play in infected water can get sick. People, including babies, with diarrhea caused by Cryptosporidia or other diarrhea-causing microbes such as Giardia and Salmonella, can infect others while using swimming pools, waterparks, hot tubs, and spas.
• Transplanted Animal Organs May Harbor Germs
  Researchers are investigating the possibility of transplanting animal organs, such as pig hearts, into people. They, however, must guard against the risk that those organs also may transmit microbes that were harmless to the animal into humans, where they may cause disease.

Some Diseases Humans Can Get Directly or Indirectly From Animals

• Anthrax - bacterial disease associated with breathing in (inhaling) the bacteria, or by coming into contact with the bacteria through cuts or abrasions in the skin, or by eating something that contains the bacteria - usually undercooked meat from an infected animal
• Bovine spongiform encephalopathy (BSE) - also called mad cow disease - infectious disease associated with cattle
• Brucellosis - bacterial disease associated with farm animals and dogs
• Campylobacteriosis - bacterial disease associated with cats, dogs, farm animals and improper food preparation
• Cat scratch disease - bacterial disease associated with cat scratches and bites
• Cryptococcosis - fungal disease associated with wild birds, especially pigeon droppings
• Cryptosporidiosis - parasitic disease associated with cats, dogs, and farm animals
• Escherichia coli O157 (E. coli O157) - bacterial disease associated with cattle and improper food preparation
• Flu virus (Influenza)
• Giardiasis - parasitic disease associated with various animals and water
• Hantavirus pulmonary syndrome - rare viral disease associated with wild mice
• Herpes B - viral disease associated with Macaque monkeys
• Histoplasmosis - fungal disease associated with bat guano (stool)
• Hookworm - parasitic disease associated with dogs and their environment
• Leishmaniasis - parasitic disease associated with dogs and sand flies
• Leptospirosis - bacterial disease associated with livestock, dogs, rodents, wildlife and contaminated water
• Lyme Disease - bacterial disease associated with dogs and ticks
• Lymphocytic Choriomeningitis - viral disease associated with rodents such as rats, guinea pigs and house mice
• Monkeypox - viral disease recently suspected to be associated with prairie dogs, Gambian rats, and rabbits
• Plague (Yersinia pestis) - rare bacterial disease associated with wild rodents, cats, and fleas
• Psittacosis - bacterial disease associated with pet birds, including parrots and parakeets
• Q fever - bacterial disease associated with cattle, sheep, goats, dogs and cats
• Rabies - viral disease associated with mammals, including dogs, cats, horses, and wildlife
• Raccoon roundworm Infection - parasitic disease associated with raccoons
• Ringworm - fungal disease associated with mammals including dogs, cats, horses and farm animals
• Rocky Mountain Spotted Fever - rickettsial disease associated with dogs and ticks
• Roundworm - parasitic disease associated with cats, dogs and their environment
• Salmonellosis - bacterial disease associated with reptiles, birds, dogs, cats, horses, farm animals, and improper food preparation
• SARS (severe acquired respiratory syndrome)
• Tapeworm Infection - parasite associated with flea infections in cats and dogs
• Toxoplasmosis - parasitic disease associated with cats and their environment
• Tularemia - bacterial disease associated with sheep and wildlife, especially rodents and rabbits
• West Nile Virus - viral disease spread by mosquitoes which can affect birds, horses, and other mammals
• Yersiniosis - bacterial disease associated with dogs, cats, and farm animals. Also associated with improper preparation of chitterlings

Prevention

• Handwashing
• Medicines
  • Antiparasitic medicines to prevent possible infection of malaria when traveling to areas where malaria is present.
  • Under specific circumstances, health care providers may prescribe antibiotics to protect people from getting certain bacteria such as Mycobacterium tuberculosis, which causes TB.
• Vaccines
  Some Vaccine-Preventable Diseases
  Caused by viruses
  • Cervical Cancer
  • Chickenpox (Varicella)
  • Flu (influenza)
  • Hepatitis A - Pronounced hep-ah-TY-tiss
  • Hepatitis B - Pronounced hep-ah-TY-tiss
  • Human Papillomavirus (HPV)
  • Measles - Pronounced MEE-zills
  • Meningitis - Viral and bacterial
  • Mumps
  • Polio (Poliomyelitis) - Pronounced PO-lee-oh
  • Rabies - Pronounced (RAY-beez
  • Rotavirus - Pronounced row-tuh-virus
  • Rubella (German Measles) - Pronounced rue-BELL-a
  • Shingles (Herpes Zoster)
  • Smallpox
  • Yellow fever
  Caused by bacteria
  • Cholera
  • Diphtheria - Pronounced dif-THEER-ee-a
  • Bacterial meningitis - rare, but can be deadly
  • Pertussis (whooping cough) - Pronounced per-TUS-iss
  • Pneumococcal pneumonia - Pronounced NEU-mo-KOK-al
  • Tetanus (lock jaw)
  • Typhoid fever - Pronounced TYE-foid
  • The form of meningitis caused by Haemophilus influenzae type B (Hib)

Traveling

When traveling, find out about other bacterial and viral diseases that are more prevalent abroad than in the United States such as Typhoid fever and Cholera. Find out which immunizations are recommended for travel to your destination(s).

References:
U.S. Department of Health and Human Services (HHS)
National Institutes of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
NIH Publication No. 06-4914
January 2006
www.niaid.nih.gov/